An OEL display panel is a display panel that uses light-emitting elements exploiting electro-luminescence of organic compounds. That is, the OEL display panel has a cathode, an anode, and organic compound-containing EL elements for electro-luminescense which are provided between the electrodes. Electro-luminescent organic compounds can be roughly classified into combinations of low-molecular organic compounds (host material and dopant material) and high-molecular organic compounds (polymer organic compounds). Examples of the electro-luminescent polymer organic compounds include polyphenylenevinylene (also referred to as PPV) and its derivatives. The OEL display panel using the electro-luminescent polymer organic compound is driven with a relatively low voltage, consumes less power and is considered to be capable of contributing to display panel size reduction; therefore, active research has been promoted.
Electro-luminescent polymer organic compounds are applied with a printing technique such as ink-jetting to respective pixels according to their color of emitting light (R, G or B). For example, for printing, an ink-jet head is used to discharge polymer inks containing such polymer organic compound and solvent. When an ink containing electro-luminescent polymer organic compound is printed in a certain pixel, it is necessary to prevent intrusion of the polymer ink into adjacent pixels.
In order to prevent intrusion of the polymer ink into the adjacent pixels, the following two methods have been employed.
A first method is to provide banks defining sub pixels in a pixel and drop a polymer ink precisely only to each sub pixel so as to prevent the intrusion of the ink into adjacent pixels.
A second method is to provide banks defining line-state pixels and banks defining sub pixels in each pixel in such a way that the former banks are higher than the latter banks defining the sub pixels, thereby suppressing intrusion of a polymer ink into adjacent pixels when it is applied to the entire region (including regions between adjacent sub pixels) of a pixel (See Patent Documents 1 and 2, for example).
A polymer ink can be readily and rapidly applied to all of the sub pixels by applying it over the entire pixel region at a time with the second method, rather than by applying it on a one-by-one basis with the first method. However, with the second method, the thickness of an organic light-emitting layer is unlikely to be uniform.
Patent Document 1: U.S. Pat. No. 6,388,377
Patent Document 2: U.S. Pat. No. 7,091,660